1. Field of the Invention
The present invention relates generally to optical switching and, more specifically, to minimizing switch latency time in an optical switching system.
2. Description of the Related Art
Data transmission technology is currently undergoing the dramatic change from electrical signal-based transmission to optical signal-based transmission. The optical revolution is providing high data transmission rates using inexpensive, reliable devices. A key advantage of optical signal technology is the ability of a single transmission line, an optical fiber, to support wavelength division multiplexed (WDM) signal transmission. WDM signals carry a number of optical signals at different wavelengths simultaneously without interference among the signals. Thus, a single optical fiber can carry simultaneously many xe2x80x9cchannelsxe2x80x9d of communication. The data of any particular such channel is expressed by the time-varying intensity of the optical signal at the channel wavelength. Typical data transmission is expressed in binary format with, for example, a low intensity representing a binary xe2x80x9c0xe2x80x9d and a higher intensity representing a binary xe2x80x9c1xe2x80x9d. Each binary value is called a bit (b). Optical networks currently support data transmission rates at a single wavelength of 2.5 to 10, gigabits/second (Gb/s), and increased data transmission rates as high as 40 Gb/s and higher are anticipated. Current Ethernet protocols utilize 512 bit data transmissions requiring 51.2 ns at a rate of 10 Gb/s.
A functional wide-area optical network exists as a connected set of distributed routing and switching nodes. User equipment can be connected to these nodes to receive and transmit data. Many communications must be transmitted simultaneously through a network. It is not feasible to permanently or globally allocate unique wavelengths to each user or particular node-to-node network connection. A flexible networking strategy is preferred which can tentatively and locally allocate a wavelength xe2x80x9cchannelxe2x80x9d to a particular data packet to be transmitted. This allows a particular data packet to traverse a network utilizing immediately and locally available channels instead of being delayed until a particular channel is globally open. Such flexibility limits the number of necessary transmission lines and the costs thereof. This strategy requires that a data packet initiated at one wavelength be seamlessly converted where necessary to another wavelength. The data-carrying intensity pattern of the output signal of such a conversion must match that of the input signal.
Recent technological advances in the characterization, production, and application of non-linear optical materials offer efficient optical wavelength conversion. Wavelength converters are available to receive a single-wavelength input signal and produce, along a conversion waveguide, an output signal at a wavelength different from that of the input signal. Each such waveguide in such a converter supports efficient conversion to a particular output wavelength. This provides a challenge to the wavelength conversion of WDM signals; namely, each single-wavelength component of a WDM signal must be separately directed to a particular waveguide which supports conversion of that component to the desired output wavelength. Furthermore, components of similar wavelength of successive packets or other data trains can be destined for conversion to different output wavelengths; thus the directing of the components must be controllable and not fixed.
Recent advances in microelectromechanical systems (MEMS) technology provide movable reflectors to support the selective directing of optical signals. However, MEMS reflectors are closed to data transmission while they are physically positioned, a process requiring a latency of 25 nanoseconds (ns) or more. Thus, while promising to provide controllable directing of single-wavelength signals to selected conversion waveguides, MEMS reflectors have lengthy switching times by optical communications standards.
What is needed in the art of optical communication switching is an optical switching system providing the wavelength conversion of each single-wavelength component of a WDM signal. Optimal switch architecture will provide rapid switch reconfiguration between converted WDM signals with minimal data flow loss.
The present invention relates to an optical switching system that includes two channel switchers. Each switcher includes an optical switch, a wavelength converter, and a multiplexer. Selectors provide and receive optical WDM signals to and from the two channel switchers in alternating fashion such that the latency time of the optical switching system is minimized to the latency time of a selector. The optical switch of an inactive switcher is configured while the active switcher converts a WDM signal.